Mixed alkaline‐earth effect on the mechanical and rheological properties of Ca–Mg silicate glasses

Abstract

In this article, we investigate the mixed alkaline-earth effect in a silicate glass series with varying the molar ratio of [MgO]/([CaO]+ [MgO]). This effect manifests itself as a minimum in Vickers microhardness (H V ), coefficient of thermal expansion (CTE), and isokom temperatures at 10 12 (T g ) and 10 2 PaÁs, and as a maximum in liquid fragility. To probe the structural origin of the mixed alkaline-earth effect in CTE and H v , we conducted the Raman measurements. In contrast to the aluminosilicate glasses, the present glass series exhibit a negative deviation of shift of peak position at~1100 cm À1 from a linear additivity, indicating the role of the aluminum speciation in affecting the vibration modes. By fitting the Vogel-Fulcher-Tamann equation to the high-temperature viscosity data, we found a near-linear increase of the fractional free volume with the gradual substitution of Ca by Mg, confirming the dynamic structural mismatch model describing the mixed modifier effect. This work gives insight into the mixed modifier effect in glassy systems. K E Y W O R D Sglass, hardness, mixed modifier effect, structure, viscosity

Mixed modifier effect in lithium‐calcium borosilicate glasses

“…37,38 For the MME, the relatively low concentration of 4coordinated boron (N 4 ) observed in the mixed modifier region ( Figure 1B) is due to the fact that the pairing of unlike modifiers is more energetically favorable to form NBO than N 4 . 32,41 According to the dynamic structure model, 7-10 a relaxation time is required to overcome the site mismatch effect while the modifiers are hopping between different ionic sites, thus resulting in the deviation from linearity in transport-related properties. 32,41 According to the dynamic structure model, 7-10 a relaxation time is required to overcome the site mismatch effect while the modifiers are hopping between different ionic sites, thus resulting in the deviation from linearity in transport-related properties.…”

Toward hard and highly crack resistant magnesium aluminosilicate glasses and transparent glass‐ceramics

“…Except for a slightly but clearly continuous shift toward lower wave numbers for the broader peak located at about 1060 cm −1 , no other important evolution appears following the gradual addition of Al 2 O 3 . The Raman modes in this region between 850 and 1250 cm −1 are tentatively ascribed to the vibrations of the polymerized tetrahedral units, although considerable controversy exists about their precise attributions . The shift of this peak center to lower wave numbers with increasing R has been attributed to the reduction in force constant, reflecting the substitution of Al for Si.…”

Mixed alkaline‐earth effects on several mechanical and thermophysical properties of aluminate glasses and melts

“…For alkaline‐earth silicate series, it is well known that alkaline‐earth cations play the role as network‐modifiers to produce non‐bridging oxygen. Considering the serious weight loss of silicate glasses when prepared using the aerodynamic levitation set‐up, we utilized the conventional melt‐quenching method to prepare the silicate glasses.…”

“…The glass fiber spinnability is sensitive to variation in the Ca/Mg ratio for the aluminosilicate glasses . The “dynamic structural mismatch model” is useful in clarifying the structural origin of mixed alkaline‐earth effect regarding mechanical and rheological properties in silicate glasses . Concerning the charge and size, Al 3+ ions lie in between network formers and modifiers .…”